1. Field of the Invention
The present invention concerns a small, large-capacitance multi-layer ceramic capacitor.
2. Description of the Related Art
Japanese Unexamined Publication No. 2006-287045 proposes to provide an electronic part having ceramic dielectric layers comprising barium titanate as a main component such as a multi-layer ceramic capacitor excellent in electric characteristic, excellent in temperature characteristic even in a case of reducing the thickness of the ceramic dielectric layer, having high reliability, reduced in the size and of large capacitance, by controlling the ratio of ceramic particles having a thickness of the crystal grain boundary present between adjacent ceramic crystal grains of 1 nm or less, among a plurality of ceramic particles constituting the ceramic dielectric layers.
The multi-layer ceramic capacitor described in the existent technique contains a glass component containing a Ba oxide, a Ca oxide, and an Si oxide, and other auxiliary components in the ceramic dielectric layer.
As other auxiliary component, one or more members selected from an Mg oxide, one or both of an Mn oxide and a Cr oxide and one or more of a V oxide, a W oxide, a Ta oxide, and an Nb oxide and an oxide of R (in which R is one or more members selected from Sc, Er, Tm, Yb, Lu, Y, Dy, Ho, Tb, Gd, and Eu, preferably, one or more members selected from Y, Dy, and Ho) are used.
The Mg oxide has an effect of flattening the temperature characteristic of electrostatic capacity and an effect of suppressing the grain growth. Further, the Mn oxide and the Cr oxide have an effect of promoting sintering, an effect of enhancing Ir (insulation resistance), and an effect of improving the high accelerated life time. The V oxide, the W oxide, the Ta oxide, and the Nb oxide have an effect of improving the high accelerated life time. The R oxide shows mainly an effect of improving the high accelerated life time.
Further, in the glass component, the Ba oxide and the Ca oxide show an effect of improving the temperature characteristic of the electrostatic capacity (rate of change of the electrostatic capacity to temperature), and the Si oxide functions as a sintering aid.
Then, the mixing amount (ratio) of the glass component raw material based on 100 mol of barium titanate is from 0.5 to 12 mol (excluding 0.5) for Ba oxide+Ca oxide and from 0.5 to 12 mol (excluding 0.5) for Si oxide when converting the Ba oxide to BaO, the Ca oxide to CaO, and the Si oxide to SiO2.
By incorporating the glass component in a predetermined range, the ratio of particles with the thickness of the crystal grain boundary of 1 nm or less or 0.75 nm or less can be controlled.
In the method of manufacturing the multi-layer ceramic capacitor, the content for each of the oxides in the dielectric substance raw material is determined so as to provide the dielectric substance porcelain described above after firing, a binder and a solvent are added and mixed to the obtained dielectric substance raw material to prepare a slurry for use in the ceramic dielectric layer and a green sheet is formed by a doctor blade method. A paste for an Ni internal electrode is printed to the surface of the obtained green sheet to prepare a ceramic sheet for a electrostatic capacity forming region having an internal electrode pattern, the ceramic sheets are laminated in plurality such that ends of the internal electrode patterns are exposed alternately to a pair of end faces of a laminate chip opposed to each other upon cutting the ceramic sheet into individual laminate chips, protecting green sheets not printed with the internal electrode pattern are laminated and crimped above and below them, and the obtained laminate is cut to a predetermined size to obtain a laminate chip, subjected to a debinding processing, fired at a programming rate of 200° C./hr, at a maintenance temperature of about 1200° C. (1180° C. to 1280° C.) for a temperature holding time of 2 hr and at a cooling rate of 200° C./hr and further annealed to obtain a sintered body.
Then, the end faces of the obtained sintered body are polished and external electrodes are coated and fired to obtain a multi-layer ceramic capacitor.
The multi-layer ceramic capacitor described in the existent technique contains an Si oxide that functions as a sintering aid being converted as SiO2 from 0.5 to 12 mol based on 100 mol of barium titanate in the ceramic dielectric layer. Accordingly, this involves a problem that the glass phase is precipitated to the crystal grain boundary in the ceramic dielectric layer by the addition of the Si oxide to exert compressive stresses on a plurality of ceramic crystal grains constituting the ceramic dielectric layer thereby lowering the permittivity further with respect to the volumic ratio of the crystal grain boundary.